We experimentally demonstrate the LWIR FSO communication with advanced modulation formats. Up to 8.4 Gbit/s PAM8 and 5.5 Gbit/s DMT transmission is achieved with 9.15-μm directly-modulated quantum cascade laser and MCT detector at room temperature.

Free space optical (FSO) communication is considered a critical part of future ICT infrastructure, particularly in non-terrestrial communication segments. In this context, the ability to achieve fast and reliable FSO propagation through long-distance atmospheric channels is the most important factor in choosing technological solutions. One property of optics directly related to this factor is the choice of wavelength. It has been identified that the mid-infrared (mid-IR) regime, which includes two atmospheric transmission windows—the mid-wave IR (MWIR, 3-5 μm) and the long-wave IR (LWIR, 8-12 μm)—can potentially offer a promising solution for achieving such performance. Additionally, viable semiconductor sources and detectors that support high-speed and efficient signal transmission are also considered critical to generating sufficient critical mass to advance the application of mid-IR FSO. Unipolar quantum optoelectronics, including quantum cascade lasers (QCL), Stark modulators, quantum cascade detectors (QCD), and quantum-well IR photodetectors (QWIP), among other components, emerge as potential candidates to build such FSO subsystems and systems. We present our recent efforts in conducting subsystem and system-level studies with different variants of these unipolar quantum optoelectronics and demonstrate the potential for feasible transmitter and receiver performance in a laboratory environment. We also discuss the key challenges and considerations of such technologies towards practical development. Finally, we summarize recent research and development efforts worldwide in advancing this highly promising direction.

Directly modulated lasers (DMLs) are widely employed in optical communications due to their significant advantages. This paper investigates a dual-κ partial corrugated grating distributed feedback (PCG-DFB) laser based on an identical active layer (IAL) structure. By introducing multiple photon-photon resonance (PPR) peaks, the -3 dB bandwidth is extended to 140 GHz. The results demonstrate that the dual-κ PCG-DFB effectively flattens the small-signal response, which is beneficial for high-speed large-signal transmission, compared to conventional single-κ PCG-DFB laser.

We demonstrate record unamplified transmissions of 256 Gbaud OOK, 155 Gbaud PAM4 and 128 Gbaud PAM6 using a C-band differential-drive SiP TW-MZM, achieving BER performance below the 6.25% HD-FEC threshold after 100 m SMF transmission.

We show a record optical amplification-free 400 Gbps PAM4/6/8 net bitrate transmission in the O-band over 500-meter SMF with performance below 6.25% OH HD-FEC threshold using 1 Vpp driving voltage on the TFLN MZM.

This paper explores photonic-based analog fronthaul solutions for 6G, highlighting their effectiveness in meeting the RF requirements of standards, supporting future distributed-MIMO networks, and providing insights into prospective solutions for radios in potential 6G bands.

We demonstrate record transmission of 256 Gbaud OOK, 175 Gbaud PAM4 and 145 Gbaud PAM6 using a C-band differential-drive silicon photonics traveling-wave Mach-Zehnder modulator, achieving BER performance below the 6.25 % HD-FEC threshold after 100 m SMF transmission.

Development of Data Center based computing technology require energy efficient high-speed transmission links. This leads to optical amplification-free intensity modulation and direct detection (IM/DD) systems with low complexity equalization compliant with IEEE standardized electrical interfaces. Switching from on-off keying to multi-level pulse amplitude modulation would allow to reduce lane count for next generation Ethernet interfaces. We characterize 106.25 Gbaud on-off keying, 4-level and 6-level pulse amplitude modulation links using two integrated transmitters: O-band directly modulated laser and C-band externally modulated laser. Simple feed forward or decision feedback equalizer is used. We demonstrate 106.25 Gbaud on-off keying links operating without forward error correction for both transmitters. We also show 106.25 Gbaud 4-level and 6-level pulse amplitude modulation links with performance below 6.25% overhead hard-decision forward error threshold of 4.5 × 10^-3. Furthermore, for EML-based transmitter we achieve 106.25 Gbaud 4-level pulse amplitude modulation performance below KP-FEC threshold of 2.2 × 10^-4. That shows that we can use optics to support (2x)100 Gbps Ethernet on single lambda at expense of simple forward error correction.

We experimentally demonstrate a room-temperature LWIR FSO link with a 9.1-μm directly modulated QCL and an MCT detector. Net bitrate of up to 16.9 Gb/s is achieved at both 15°C and 20°C over a 1-meter distance.

We experimentally demonstrate a room-temperature LWIR FSO link with a 9.1-μm directly modulated QCL and an MCT detector. Net bitrate of up to 16.9 Gb/s is achieved at both 15°C and 20°C over a 1-meter distance.